Because of their low cost and ease of use, plastic materials, such as epoxy resins, are increasingly employed for encapsulating electronic devices. The encapsulating material may be used, for example, to reinforce the solder interconnections of a chip to a ceramic substrate. It is often necessary, however, to remove the epoxy encapsulant to inspect, test or repair the electronic device. In the prior art, various methods and apparatuses are employed for decapsulation of electronic devices.
U.S. Pat. No. 3,969,813 discloses a process and apparatus for removing encapsulant from about a semiconductor chip using a jet nozzle with a plurality (e.g. four) of precisely directed sprays which strike the encapsulant to effect removal of the chip. The chips being removed are mounted on a ceramic substrate.
U.S. Pat. No. 4,359,360 discloses an apparatus for jet etching a plastic encapsulant. The apparatus employs turbulent flow of the etchant, causing great agitation of the etchant to remove the encapsulant. The flow of the etchant is controlled by means of a vacuum source.
U.S. Pat. No. 4,384,917 discloses an apparatus for jet etching an encapsulated electronic device. The apparatus uses a partial vacuum to control the flow of the etchant. The entire electronic component to be decapsulated is exposed to the etchant.
Most of the conventional methods for decapsulating plastic packages, such as the jet etch method, require the use of chemical, plastic etching agents. The most common etching agents include hot concentrated acids such as nitric acid and sulfuric acid. The jet etch method requires the use of large quantities of concentrated acid. In addition, the concentrated acid must be used at a high temperature. As a result, conventional jet etch methods are costly, as well as potentially hazardous to personnel.
It is, therefore, an object of the present invention to selectively remove plastic encapsulant from about and under an electronic component which is adhered to a carrier without damage to the carrier and without the use of large quantities of chemical etchants.